What is the power factor of an LCR series circuit at resonance?

In an LCR-series a.c. circuit, the current

What do you mean by power factor of an a.c. circuit ?

What is impedance of circuit at resonance ?

What is the significance of Q factor in a series LCR resonant circuit?

The power factor of an a.c. circuit having resistance R and indctace L (connected in series) and an angular velocity omega